optimize: raft metadata api

[funky-eyes]

• I have registered the PR changes.

Ⅰ. Describe what this PR did

Ⅱ. Does this pull request fix one issue?

Ⅲ. Why don't you add test cases (unit test/integration test)?

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[codecov]

Codecov Report

Attention: Patch coverage is 25.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 52.28%. Comparing base (785b20c) to head (dd9c7bb).
Report is 1 commits behind head on 2.x.

Files with missing lines	Patch %	Lines
...scovery/registry/raft/RaftRegistryServiceImpl.java	25.00%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x    #6852      +/-   ##
============================================
- Coverage     52.32%   52.28%   -0.04%     
- Complexity     6413     6414       +1     
============================================
  Files          1083     1083              
  Lines         37918    37918              
  Branches       4494     4494              
============================================
- Hits          19839    19827      -12     
- Misses        16109    16122      +13     
+ Partials       1970     1969       -1     

Files with missing lines	Coverage Δ
...a/org/apache/seata/common/util/HttpClientUtil.java	36.58% <ø> (ø)
...scovery/registry/raft/RaftRegistryServiceImpl.java	17.69% <25.00%> (ø)

... and 3 files with indirect coverage changes

[xingfudeshi]

LGTM